The present invention relates to coating compositions; especially solvent borne coating compositions which include a reactive diluent comprising 1,3-cyclohexane dimethanol and 1,4-cyclohexane dimethanol.
Coating compositions having a high concentration of solids (xe2x80x9chigh solids compositionsxe2x80x9d) are becoming increasingly popular due to environmental regulations that limit the volatile organic solvent content in such compositions. High solids compositions contain high levels of non-volatile materials such as film-forming polymer, pigments, and fillers and low levels of organic solvent.
At present, it is difficult to formulate high solids compositions having acceptable viscosities. If the viscosity of the coating composition is high, it is difficult to spray apply the coating composition and the appearance of the applied coating is less than ideal.
Several unsatisfactory solutions have been proposed to provide high solids compositions having acceptable viscosities. One proposed solution is to use low molecular weight film-forming polymers to form the coating composition because, generally, low molecular weight polymers have low viscosities. The problem with using low molecular weight polymers is they give rise to soft coating films that have unacceptable dust free times (the time period from when a coating composition is applied to when the dust no longer adherers to the coating).
Another proposed solution has been to add a viscosity modifying additive to the coating composition. Viscosity modifying additives are well known. Common viscosity modifying additives comprise a low molecular weight compound or polymer such as a polyester. Unfortunately, coating compositions that contain viscosity modifying additives can be unacceptably soft.
An example of a viscosity modifying additive is disclosed in U.S. Pat. No. 5,541,268. The disclosed viscosity modifying additive is a hard to dissolve solid When the solid is dissolved and placed in solution, it often crystallizes out very quickly. Consequently, it is difficult to use the viscosity modifying additive disclosed in U.S. Pat. No. 5,541,268 in liquid coating compositions.
The present invention provides a solvent borne coating composition that has acceptable viscosities and superior performance properties such as hardness, dust free time, etc.
The present invention is a coating composition comprising:
a. at least one hydroxyl functional polymer;
b. a crosslinker capable of crosslinking with said hydroxyl functional polymer (a) to form a film;
c. a reactive diluent comprising:
i. 1,3-cyclohexane dimethanol, and
ii. 1,4-cyclohexane dimethanol; and
In another embodiment, the present invention is a method of coating an article comprising the steps of:
a. applying over the article a coating composition comprising:
i. at least one hydroxyl functional polymer,
ii. a crosslinker capable of crosslinking with said hydroxyl functional polymer to form a film,
iii. a reactive diluent comprising:
(A) 1,3-cyclohexane dimethanol, and
(B) 1,4-cyclohexane dimethanol, and
b. curing the composition.